Power tools used to drive a screw or other threaded fastener by way of a bit or other end tool, and having a light, are now common. When the power tool is used in a dark place, the light illuminates both the fastener being affixed to the workpiece, and the bit used to drive the fastener, thereby making it easier to use the power tool in dark places.
More specifically, as shown in FIG. 14, this power tool 401 has a body 410, and inside the body 410 has a motor not shown as the drive source, and mechanical parts not shown for transferring torque from the motor not shown. An end output unit not shown is housed near the distal end inside the body 410, and a tool chuck 411 is disposed to this distal end. The tool chuck 411 is drivably linked to the end output unit not shown, and an end tool is chucked in the tool chuck 411. The end output unit not shown is drivably linked inside the body 410 to the motor not shown through the mechanical parts not shown, torque from the motor is thereby transferred to the end output unit, and the end output unit is thus driven. By thus driving the chucked end tool not shown, the screw or other fastener can be tightened to the workpiece or loosened.
A handle grip 410C that is gripped by the user when using the power tool is rendered integrally to the body 410. A pull trigger 413 for starting and stopping driving the motor not shown is disposed at the top part of the handle grip 410C. As shown in FIG. 14, a light unit 420 is externally affixed to a position on top of the body 410. The light unit 420 has a light-emitting element not shown, and can thereby illuminate a fastener not shown that is driven by the end tool not shown. A battery pack 412 is also disposed at the bottom part of the handle grip 410C. This battery pack 412 houses a battery not shown that is the power source for supplying power, and the battery not shown is electrically connected to the motor not shown.
When constructing wood-frame houses, wood members are often fastened with metal fasteners in confined spaces. With the prior art power tool 401 described above, however, the light unit 420 is disposed externally at a position on the top of the body 410 as described above, and the light unit 420 therefore often gets in the way and makes attaching fasteners difficult. Japanese laid open Utility Model application publication No. H1-117882 teaches as a power tool solving this problem a power tool 501 having a light unit 520 disposed externally to the body 510 in front of the trigger 513 as shown in FIG. 15.
With the conventional power tool 501 described in the Japanese Utility Model application publication No. H1-117882, however, the light unit 520 interferes with the index finger of the user operating the trigger 513 because the light unit 520 is disposed externally to the body 510 in front of the trigger 513. To solve this problem, laid open Japanese Utility Model application publication Nos. S55-151409 and H3-79279, and laid open Japanese Patent Application publication No. H10-44064 teach power tools having a light unit rendered not at a position on the top of the body nor at a position in front of the trigger, but at a position externally to the body in the vicinity of the end output unit or at the bottom of the grip.
In each of the power tools described above, however, the lighting angle of the light unit is fixed. The tools chucked into the end of such power tools, however, vary in length from 60 mm to 150 mm. A problem here is that because the lighting angle is fixed with such conventional power tools, light cannot always thrown onto the fitting between the bit and the head of the screw used as the fastener, or on the tip of the screw, when the bit is changed, and it becomes difficult to see.
Furthermore, because the light unit is fixed directly to the body, vibration produced when using the power tool can result in continuity failures in the light-emitting element or wiring failures.
In order to avoid this problem, Japanese laid open Patent Application Publication No. 2001-300867 discloses a power tool in which the light unit has a flexible shaft extending from the bottom of the handle grip. A light-emitting element is disposed at the distal end of this flexible shaft. Because the flexible shaft can be bent to any desired direction, the lighting angle of the light-emitting element can be freely adjusted.
A problem with the conventional power tool described in the Japanese Patent Application Publication No. 2001-300867, however, is that vibration produced from using the power tool causes the light from the the light-emitting element to waver because the lighting angle of the light-emitting element is held by the flexible shaft, and it is difficult to see the target.
Furthermore, power tools described in Japanese Utility Model application Kokai Nos. H3-79279, H1-117882 and S55-151409 have a switch for turning illumination from the light-emitting element on and off. If, for example, the user forgets to turn the switch off, the battery is consumed even though the light is not being used, and the light then may not turn on when it is actually needed.
Yet further, with each of the conventional power tools described above the light-emitting element projects light from only one direction. As a result, the light casts a shadow of the end tool onto the workpiece when the bit is fit into the screw head, making it difficult to see. Furthermore, white incandescent lights are generally used for the light-emitting element in the prior art, but contrast is low and a relatively high wattage incandescent light must be used to achieve sufficient brightness. The power supply must therefore become bulky, and this degrades operability.
Furthermore, when working in high, dimly lit places on a stepladder, for example, there is no place to set the power tool. A hook is therefore needed to hang the power tool on the user's belt or ladder, for example, when it is not being used. However, providing both a hook and a light unit on the power tool increases both the size and cost of the power tool.
Therefore, an object of the present invention is to provide a power tool having a light unit that does not get in the way, and which enables adjusting the lighting angle of the light unit without the emitted light shaking.
A further object of the invention is to provide a power tool that prevents depletion of the power supply due to the light switch of the light unit not being turned off.
A yet further object of the invention is to provide a power tool that is resistant to continuity failures in the light-emitting element and interruptions in wiring members.
A yet further object of the invention is to provide a small, economical power tool.
A yet further object of the invention is to provide a power tool providing high contrast illumination and capable of minimizing generation of a shadow of the end tool.